Replace, test question

*To*: mathgroup at smc.vnet.net*Subject*: [mg120305] Replace, test question*From*: PA32R <tio540s1 at gmail.com>*Date*: Mon, 18 Jul 2011 06:13:23 -0400 (EDT)

I'm very new to Mathematica and trying to work my way through it. I don't understand why: {58, 61, 15, 66, 10, 2, 24, 81, 45, 84} /. x_ /; PrimeQ -> P returns: {58, 61, 15, 66, 10, 2, 24, 81, 45, 84} I would expect it to take the list, replace everything in the list that matches any pattern and passes the PrimeQ test, i.e., is prime, with P to yield: {58, P, 15, 66, 10, P, 14, 81, 45, 84} Can someone explain my misunderstanding? Thanks.

**Follow-Ups**:**Re: Replace, test question***From:*Heike Gramberg <heike.gramberg@gmail.com>

**Re: Replace, test question***From:*DrMajorBob <btreat1@austin.rr.com>

**Re: Replace, test question***From:*Tomas Garza <tgarza10@msn.com>